Drying of colors, lacquers, and the like on metal bodies



Feb. 22, 1955 c. A. H. SCHMIDT 2,702,847

DRYING OF COLORS, LACQUERS, AND THE LIKE ON METAL BODIES Filed July 12, 1951 2 Sheets-Sheet l J fig. 2/

. I I I m VENTOR CONSTANTIN A. H. SCHMIDT ATTORNEYS Feb. 22, 1955 Q sc 2,702,847

LIKE ON METAL BODIES DRYING OF COLORS, LACQUERS, AND ThEI 2 Sheets-Sheet 2 Filed July 12, 1951 CONSTANTIN A. H SCHMiDT BY M fizz A TTORNEYS.

States DRYING OF COLORS, LACQUERS, AND THE LIKE N METAL BODIES Constantin A. H. Schmidt, Stuttgart-Bad Cannstatt, Germany This invention relates to a method of and apparatus for the drying of colours, lacquers, artificial resin layers or the like on metallic hollow bodies of irregular form, particularly on vehicle bodies for motor vehicles.

It has already been proposed to dry freshly lacquered sheet-metal bands, for example dynamo laminations, by resistance heating by means of electrical eddy currents induced in them, that is by carrying them in afiat condition through an electrical or magnetic alternating current field. However, this proposal has not been successfully extended to the rest of the coating field, as there were cheaper methods for the drying of such simple flat sheetmetal formations over which the proposed method offered no particular advantages. But it was overlooked that these customary methods, in which theheat is produced outside the body to be dried, and is only transmitted to the same by separate heat carriers, for example by warm air, required considerably more expenditure of space, time and cost of apparatus in the case of sheet-metal bodies with large surfaces and irregular shapes, such as in the case of vehicle bodies for motor vehicles, and that in this field very considerable economic advantages can be achieved by the production of the drying heat directly in the sheet-metal wall of the body by the use of appropriate apparatus.

The invention accordingly resides in the use of the per se known drying process in an electrical or magnetic alternating field for the drying of colours, lacquers, artificial resin layers or the like upon metallic hollow bodies with a large surface and of irregular shape, especially upon vehicle bodies for motor vehicles and in the provision of apparatus suitable for this purpose.

Further objects and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows for purposes of illustration only 2,702,847 Patented Feb. 22, 1955 sectional shape substantially corresponds to that of the vehicle body, so that the Winding surrounds the body, located in it, on all sides with a clearance which is as small as possible, but which excludes direct contact with the freshly lacquered surfaces. In order to keep th1s clearance as small as possible also at the tapered ends of the vehicle body, the winding 14 consists of three parts, namely a fixed middle part 15 having boundary surfaces disposed substantially parallel to one another and the end parts 16 and 17 tapering respectively towards the front and rear. The two end parts are constructed so that they can be swung in the directions of the arrows 18 and 19 respectively as shown in Fig. 2, whereby they can be swung out of the way for the run in and out of the vehicle body 10. In the drawing the individual parts of the winding are shown diagrammatically only. In practical execution, each part will naturally, for reasons of strength, be wound by itself upon a light, thin-walled, insulating body, for example of hard pasteboard, by which the heat produced in the wall of the vehicle body is at the same time retained.

When the freshly lacquered vehicle body has been run into the winding and the latter has been closed, an alternating current is conducted through the turns of the three winding parts whose voltage and frequency are so designed in relation to the number and Wire size of the turns that the alternating field produced by it gives rise in the sheet-metal wall of the vehicle body to induced currents of sufiicient strength to bring the sheet-metal wall, by resistance heating, in a short time to the temperature necessary for the rapid drying and hardening. of thelacquer coating and to maintain it at this temperature for a sufiiciently long period. As, for the last-named purpose, only the heat lost by radiation to the outside need be replaced and as this is only very slight due to the complete enclosure of the vehicle body by the winding, a large part of the winding can already be switched off after the attainment of the drying temperature. Furthermore, the heat developed in the winding itself protects the vehicle body to a considerable extent against radiation to the outside. When the drying of the lacquer coating on a vehicle body is completed, the current is completely switched ofi, the winding is opened by swinging out the parts 16 and 17 and the vehicle body is run forwardly out of the winding. Immediately thereafter, the next vehicle body can be run into the winding, whereby the heat stored up m the insulatmg bodies serving as windingcarriers is also several preferred embodiments of the present invention and wherein Fig. 1 is a side view of one embodiment in accordance with the present invention,

Fig. 2 is a top plan view of the embodiment shown in Fig. 1,

Fig. 3 is an end view of a modified embodiment in accordance with the present invention,

Fig. 4 is a transverse cross-sectional view of still another embodiment in accordance with the present invention,

Fig. 5 is a longitudinal cross-sectional view of another modification in accordance with the present invention,

Fig. 6 illustrates still another modification of the present invention,

Fig. 7 is a top view with parts broken away showing a further modification of the present invention for use with assembly lines, and

Fig. 8 is a cross-sectional view of Fig. 7 taken along lines 8-8 thereof.

Figs. 1 and 2 illustrate in side elevation and plan view an arrangement in which the object to be dried, in the 7 present case a vehicle body ltl with a sheet-metal outer skin for a motor vehicle, is secured to a travelling undercarriage 11. The rollers 12 of the undercarriage are guided on rails 13 which form a part of the production line for the production of the vehicle body. The vehicle body provided in the production line with a layer of colour or lacquer is moved for its drying into a winding 14 of good-conducting metal wire whose mutually insulated turns are carried under the rails 13 and whose crossutilised for the next drying operation. In this fashion, the successive drying of a large number of vehicle bodies on the production line can be performed with a very small expenditure of time, space and electrical current.

In the example illustrated in Fig. 3, the winding is replaced by one or more yoke-shaped field magnets 24) arranged one after the other in the longitudinal direction of the production line 13, which magnets are excited by the field winding 21 likewise by alternating current and whose pole shoes 22, 23, 24 conform at their faces presented toward the vehicle body 10 to the shape of the outer wall of the vehicle body. The pole shoes 22, 23 and 24 are displaceable in the magnet frame transversely of the production line, so that they can be brought com.- paratively close to the wall of the vehicle body for the drying of the lacquer coating, but can be moved sufficiently far from it to allow of the running in and out of the vehicle body. a

After the exciting current has been switched on, the sheet-steel wall of the vehicle body located between the pole shoes forms, so to speak, the armature traversed by the alternating magnetic flux, in which armature suificrent heat for the drying of the lacquer coating is continuously produced by the eddy currents induced in the wall opposite to each pole shoe and also by the constantly alternating magnetisation of the sheet-metal surfaces. The windings 21 of the individual are so wound or connected that the eddy current induced by adjacent magnets in the sheet-metal wall are always similarly directed at the edges of the pole shoes 22, 23 and 24 and that in particular strong and similarly directed induced currents are produced around the window and door openings of the vehicle body. The iron core 25 of the magnet .is

naturally considerably sub-divided in the usual fashion. For example it may be composed of sheet-metal strips insulated from one another in order to keep as low as possible the current losses due to its remagnetisation.

In the example of Fig. 4, the iron masses are completely dispensed with, the .electromagnets having been replaced by spirally wound fiat windings 26 which conform to the shape of the outer surfaces of the vehicle body and which are displaceable transversely in relation to the sheet-metal wall of the vehicle 10. Due to the eddy currents induced in the sheet-metal wall after the switching on of the exciting current, sufficient heat is produced to dry the lacquer coating of the vehicle body in a short time. In this case, also, provision is made by appropriate connection of the windings 26 to ensure that the induced currents are in the same direction in the marginal regions. In order to produce particularly strong eddy currents around the window openings 2'7 of the vehicle body, short solenoids 28 whose cross sectional shape conforms to that of the window opening are inserted in these openings.

Figs. and 6 show arrangements in which the en- .ergising windings are disposed solely in the interior of the vehicle body to be dried. For this purpose, in the case of the vehicle body shown in Fig. 5, which is closed on its underside by a sheet-metal floor 29. use is made of lon itudinally extended solenoids 3t), 31 with horizontal longitudinal axes, one of which is introduced into the vehicle body through the window opening 32 for the windscreen and the other through the opening 33 for the rear lu gage boot, so that the two s lenoids are located parallel to each other, substantially filling the entire interior of the vehicle body. In this case also, the solenoids are wound upon appropriate supporting bodies of insulating material and are so connected that the exciting current circulates in them in the same direction in each case. By this means, the result is achieved that the interior space between the windings remains substantially free from induction. but that the two windings assist each other in their induction effect towards the outside. but so that strong induced currents circulating about the longitudinal axis of the vehicle body ll are produced in the sheet-metal wall of the said body. In this case also, as in Fig. 4, short solenoids 28 may be introduced into the lateral window openings of the vehicle body in order to induce additional eddy currents around these openings.

The example of Fig. 6 is concerned with a vehicle body open at its u derside such as is used for motor vehicles in which the floor forms a com onent part of the vehicle frame. In this case, the vehicle bodv sus ended on a hoist by means of an arran ement 34 is di ped into a lacquer bath and after draining is placed from above on an ener ising winding 35 whose turns are disposed with a vertical winding axis upon a supporting body conformin to the shape of the vehicle body. In cases. a field winding of the same kind may be disposed externally around the vehicle body. either alone or in addition. this winding then being placed over the body from above bv means of a hoist.

An installation suitable for the simultaneous drying of a number of vehicle bodies is illustrated diagrammaticallv in Figs. 7 and 8. This installation consists essentially of a circular-like superstructure 37 which is arran ed on a turntable 36 and which is divided by radial partitions 38 into sector-shaped drying com artments Of the freshly lacquered vehicle bodies 14) secured to trav ino 11m'lerCallla"6S 11. there is alwa s one. on the track 13 forming the production line. in front of an empty opened drying compartment 39. This is turned through 90 on a turntable 49 provided in this track and is run into the drying compartment on a transverse track 41 leadin into the said compartment. A horizontal winding 30 which is secured to the inner wall 42 of the cornpartment and corresponds to the upper solenoid in Fig. is thereby caused to penetrate through the windshield opening far into the interior of the vehicle body. The swingable side walls 38 of the compartment are then swung towards the vehicle body so that the short solenoids 28 (see Fig. 4) attached to them enter into the sidewindow openings of the vehicle body. Finally, the outer wall 45 of the compartment mounted on a travelling undercarriage 44 is run on the track 41 up to the free ends of the side wall of the compartment and is locked thereto. A long winding 31 which is secured horizontally to the outer wall 45 and which corresponds to the lower solenoid in Fig. 5 is thus caused to enter through the rear opening of the luggage space of the vehicle body far into the interior of the said body. By the lockmg of the side walls 38 and the outer wall 45 of the compartment, the current-conducting connections between the individual windings of the box in question and the source of current are at the same time established, so that the drying process in the closed compartment proceeds with the minimum loss of heat. In the meanwhile, the turntable 36 is turned together with the drying compartment on it, in steps until, at each step, the next compartment comes opposite the turntable 40. The outer wall 45 of this compartment is then run on the cross track 41 into the open position and a dried vehicle body 10 is run over the turntable 4-0 out of the compartment and on to the production line 13 where it continues its progress in the direction of the arrow 46 for its further treatment. The next vehicle body to be dried is now run, in the above described manner, into the unoccupied compartment from the other side of the production line. Having regard to the interval at which the freshly lacquered vehicle bodies travel along the production line, the number of compartments is so selected that the individual vehicle bodies are each completely dried after a full revolution of the turntable 36. A central suction plant continuously draws oft from the compartment the solvent vapours evolved in the individual compartments during the drying process. The electrical part of the installation, such as transformers, frequency changers, switch gear and the like, may be accommodated in the central cylindrical space 47 of the roundabout structure where it can be sealed in a safe fashion as regards fire and explosion.

The frequency of the alternating current to be employed may vary from that of the normal alternating current supply up to high frequencies (Tesla currents). In general, in cases in which the field windings or pole shoes can be made to conform very closely to the contours of the body to be dried, particularly also in the case of thick-walled bodies, lower frequencies Will be chosen in order to transmit as large quantities of heat as possible to the body to be dried with the simplest possible means and without leakage current losses. Where the shape of the bodies to be dried does not permit of such close approach of the energising means to all of the individual surfaces, for example in the case of the use of a single arrangement for bodies of different shape, use in preferably made of arrangements which operate with highfrequency currents and are capable of wider radiation undesirable leakage radiation to the outside being limited, if desired, by reflecting surfaces, surrounding the windings or magnets, of tin foil or of diamagnetic materials or in any other known manner.

What we claim is:

1. Method for the drying of layers of color, paint, lacquer, artificial resin or the like, on hollow metal bodies with a large surface and irregular shape, particularly the metal outer skins of bodies for motor vehicles by the use of means for producing alternating magnetic or electrical fields, comprising the steps of drying said hollow metal bodies by inducing eddy currents therein by energiza-tion of said means for producing alternating magnetic or electrical fields, individually applying the cur rents adjacent the form of the body to be dried, and selectively placing some of said means for producing the alternating fields adjacent the hollow body to be dried through openings therein and placing the hollow body open at one side over some of said means for producing the alternating fields.

2. Arrangement for carrying out the method according to claim 1, comprising means for producing alternating fields shaped to conform closely to the formation of the body to be dried, th eddy currents being induced by said is for "roducing the alternating fields, said means "eing divided with the parts thereof made movable in relation to one another in order to permit the introduction of said means into the hollow body or the placing of the hollow body over said means, so that they can be brought from the outside or from the inside as closely as possible to all the parts of the walls of said body.

3. Arrangement according to claim 2 for the drying of a body for a motor vehicle, comprising an intermediate, fixed, main portion conforming to the maximum cross section of the vehicle body and two movable end portions tapering towards the ends of the vehicle body.

4. Arrangement according to claim 2 for the drying of the body of a motor vehicle, wherein the pole shoes of electromagnets producing the alternating fields or fiat windings, wound spirally, producing the alternating fields are shaped to conform to the arched outer surfaces of the vehicle body and are made displaceable transversely in relation to the surfaces.

5. Arrangement according to claim 4, wherein adjacent winding par-ts or magnet parts are so connected that the induced currents produced by them in common marginal regions How in the same direction.

6. Arrangement according to claim 5, wherein provision is made for inducing particularly strong currents at the edges of openings in the body to be dried, by coils projecting into these openings.

7. Arrangement according to claim 6, wherein coils introduced parallel to each other into the interior of the body to be dried are connected in such a manner that the exciting currents in them circulate in the same direction.

8. The arrangement according to claim 1 for the simultaneous drying of a plurality of vehicle bodies comprising a rotatable, substantially circular superstructure, a turntable 'for said superstructure, said superstructure having a plurality of sector-shaped drying compartments for individual bodies, means including a plurality of windings producing alternating fields secured to the walls of the drying compartments which, at least in part, are swingably and displaceably mounted, said means being shaped to conform closely to the shape of the body to be dried so that they may be brought from the outside or from the inside as closely as possible to all the parts of the walls of said body.

9. Arrangement according to claim 7, wherein said operable drying means includes a plurality of windings, a source of current and current-conducting connections between at least some of said windings themselves and between the windings and said source, and wherein the current-conducting connections between the Winding themselves and between the windings and the source of current are produced simultaneously with and by means of locking operations for securing the movable compartment walls.

10. Arrangement according to claim 9, wherein the electrical parts of the combination including transformers, frequency converters, switches and the like, are accommodated in a central space provided in said first-mentioned means comprising a turntable.

11. In the continuous process of drying large coated surfaces such as automobile bodies, means comprising a turntable, having a series of radially spaced drying compartments, each of said compartments having independently movable pivotal side walls and an outer end wall, operable drying means on said walls adapted to be laid close to the inner and outer surfaces of such body, means for rotating said turn-table, carriage and track means for each of the compartments, turnable means adjacent .the turntable for each of the bodies before and after drying thereof, and track means leading to and from the turnable means.

12. Method for drying coatings of paint, lacquer, enamel or synthetic resin on the outer plating of automotive vehicle bodies by inductive heating, characterized by the fact that at least a part of the induction coils for the inductive heating are movable with respect to the vehicle body and at least a part of the movable coils is introduced through openings present in the vehicle body for doors, windows and the like, transverse to the wall of the vehicle body into the inside of said body.

References Cited in the file of this patent UNITED STATES PATENTS 1,555,860 Ledwinka Oct. 6, 1925 1,873,808 Bailey Aug. 23, 1932 2,040,884 Somes May 19, 1936 2,052,010 Bailey Aug. 25, 1936 2,182,799 Farr Dec. 12, 1939 2,267,001 Toulmin, Ir Dec. 23, 1941 2,387,516 Kaminski Oct. 23, 1945 2,504,198 Jagen Apr. 18, 1950 2,511,059 Haynes June 13, 1950 FOREIGN PATENTS 578,757 Great Britain July 10, 1946 

12. METHOD FOR DRYING COATING OF PAINT, LACQUER, ENAMEL OR SYNTHETIC RESIN ON THE OUTER PLATING OF AUTOMOTIVE VEHICLE BODIES BY INDUCTIVE HEATING, CHARACTERIZED BY THE FACT THAT AT LEAST A PART OF THE INDUCTION COILS FOR THE INDUCTIVE HEATING ARE MOVABLE WITH RESPECT TO THE VEHICLE BODY AND AT LEAST A PART OF THE MOVABLE COILS IS INTRODUCED THROUGH OPEININGS PRESENT IN THE VEHICLE BODY FOR DOORS, WINDOWS AND THE LIKE, TRANSVERSE TO THE WALL OF THE VEHICLE BODY INTO THE INSIDE OF SAID BODY. 